Laser modules used as light sources in applications such as projectors that project multicolor images, for example, incorporate laser light sources of three colors, red, green, and blue (RGB). Among others, in volumetric displays or the like that project stereoscopic images, a plurality of LD (Laser Diode) devices of the same wavelength must be provided in order to project (spatially multiplex) images at different depth positions for each color. In such applications, therefore, a laser module having multiple LD arrays, one for each wavelength, is used as the light source device.
Since a batch of LD devices produced as laser light sources generally contains a certain percentage of defectives, a burn-in test for sorting out early defectives by measuring various characteristics while driving the LD devices in a high-temperature environment is conducted at the time the laser module containing the LD devices is fabricated.
Patent document 1 discloses a burn-in apparatus for performing the burn-in of integrated semiconductor laser devices. The burn-in apparatus includes a thermostatic chamber capable of accommodating a plurality of integrated semiconductor laser devices, photodiodes each for receiving light emitted from a corresponding one of semiconductor lasers, laser connecting lines each connected to the p-side electrode of each individual one of the semiconductor lasers, a multichannel selector for selecting lines that supply current from among the laser connecting lines, PD connecting lines each connected to each individual one of the photodiodes, a multichannel power supply for supplying current to the laser connecting lines selected by the multichannel selector, and a temperature controller for controlling the temperature of the thermostatic chamber.
Patent documents 2 and 3 each disclose an array-type laser module for optical communications which is constructed by arranging LD arrays, arrayed optical waveguides, optical fiber arrays, etc., on a substrate. In the case of laser modules for optical communications, LD devices of different wavelengths are configured into arrays in order to perform wavelength multiplexing. In such optical communications laser modules, if even one of the LD devices is rendered defective, the whole module will be rendered defective because the wavelength corresponding to that LD device cannot be obtained. In view of this, in order to increase the percentage of non-defective laser modules, it is known to design the LD array with redundancy by accounting for the production yield, so that non-defective devices are selected from the LD array and only the selected devices are optically coupled to an optical fiber array (for example, refer to patent documents 4 and 5).
Patent document 4 discloses an optical array link module which includes an LD array constructed by arraying a plurality of LDs the number of which is made larger than the required number of channels by accounting for a certain percentage of defectives, an optical fiber arrayed cable constructed by arraying optical fibers one for each LD, and a lens array constructed by arraying lenses one for each LD and interposed between the LD array and the optical fiber arrayed cable so as to optically couple the LD array to the optical fiber arrayed cable in a desired manner. In this module, any optical fiber corresponding to a defective LD in the LD array is cut to isolate the defective, and the optical fibers equal in number to the desired number of channels are used as working fibers.